<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <select>
    <option value="1">北齐</option>
    <option value="2">庆国</option>
    <option value="3">北liang</option>
  </select>
  <script>
    // 下拉表单选中的值, 是选中的option的value
    const select = document.querySelector('select')
    select.addEventListener('change', function(e){
      console.log(e.target.value);
    })
  </script>
</body>
</html>